Mechanical ventilation (MV) is a life saving therapeutic approach for patients with acute lung injury. However, this procedure represents a major cause of iatrogenic lung damage in intensive care units. Inflammation is known to be involved in the pathogenesis of the ventilator-induced lung injury (VILI) but many aspects and mediators of this process are unknown. We showed previously that MV promoted pulmonary histopathological changes underlined by a drastic alteration in local gene expression profile and that the augmented expression of the long pentraxin Ptx3 drastically accelerates the development of VILI. The aim of this study is to investigate the role of Ptx3 in VILI.  It was addressed to evaluate the protein expression of inflammatory mediators in the sera and lungs of Ptx3-transgenic (Tg(Ptx3)CD1) and knockout (Ptx3^-/-) mice submitted to high tidal volume ventilation.

PTX3 transgenic (Tg(Ptx3)CD1) and knock-out (Ptx3^-/-) mice and related wild type (Wt) mice (n= 12 mice/group) were ventilated with 45ml/kg of tidal volume until respiratory system Elastance increased 50% (Ers150%) of its initial value (criteria indicative of VILI), or alternatively ventilated for 20’, 40’ and 60’. At indicated time point, lungs were collected and prepared for protein expression analysis. Systemic levels of the inflammatory mediators involved in VILI, were assessed in the serum by ELISA and the local production by immunohistochemistry using a tissue microarray (TMA) representative of the peribronchiolar, median and subpleural regions of the right lung collected from the 84 mice included in the study. The citoplasmatic staining of epithelial bronchiolar and alveolar cells, endothelia and pneumocytes were analysed by the ACIS^® III system (Dako's pharmDx™), and results are expressed as staining intensity level.

Here we show that at the time respiratory Elastance augment 50% from its basal level (~70 min in Tg(Ptx3)CD1 and ~140min in Ptx3^-/- mice) the local increased Il1b protein levels parallels the gene expression pattern. The lower levels of Il1b in Ptx3^-/- in comparison with Ptx3^+/+ ventilated mice ascertain for the amplification loop of Il1b expression promoted by Ptx3. At this time point, although Tnfa lung levels in Tg(Ptx3)CD1 showed a significant decrease when compared to non-ventilated mice they remained close to the basal concentration in all groups which was also observed for Ptx3 serum levels between ventilated-Ptx3^+/+ and non-ventilated counterparts. Preliminary IMH data are indicative of major alterations in Il1b and Tnfa expression in the epithelial bronchio-alveolar cells of the peri-bronchiolar region in both Ptx3 transgenic and knockout mice.

The findings presented here support the data that the local and not systemic, temporal-regulated-balance of inflammatory mediators in the lungs plays a preponderant biological role in initiating an inflammatory cascade in the alveolar space and corroborate the central role of Ptx3 in VILI.